The UCB Comedy Improv Manual by Matt Besser, Matt Walsh, and Ian Roberts Out Now
When considering who are the modern masters of improvisational comedy/who should write an instructional book on improv, a good place to start with that list is the founders of The Upright Citizens Brigade.
Luckily, that just happened as Matt Besser, Matt Walsh, and Ian Roberts, ¾ of the original UCB 4 (the other one if Amy Poehler and we’re guessing she’s got a little busy with everything she’s doing to join in here) have written and released an instructional book on long form improvisational comedy.
If you have any interest in improv to any degree, The UCB Comedy Improv Manual just might be a good thing to buy.